Nouvelle cible pour le traitement du cancer du sein.

In a research study published in the journal Oncogene, scientists from Sylvester Comprehensive Cancer Center at the University of Miami Miller School of Medicine showed that by therapeutically targeting the receptor for advanced glycation end-products (RAGE) in breast cancer cells, they decreased tumor growth, reduced tumor angiogenesis and recruitment of inflammatory cells, and dramatically decreased metastasis to the lung and the liver.

"RAGE is highly expressed in various cancers and is correlated with poorer outcome in breast and other cancers," said Barry I. Hudson, Ph.D., cancer researcher at Sylvester, assistant professor of medicine at the Miller School, and corresponding author of the study. "In this study, we tested the role of targeting RAGE by multiple approaches in the tumor and tumor microenvironment, to inhibit the metastatic process."

Over the past few years, Hudson and his team have found that blocking RAGE signaling may be an attractive therapeutic target for reducing tumorigenesis and metastasis. Their work has demonstrated that blocking RAGE signaling results in reducing tumor growth and metastasis. Furthermore, they have shown activation of RAGE signaling results in profound changes in cellular properties strongly associated with the metastatic process including increased cell migration and invasion, proliferation, and resistance to apoptosis.

"The results of the study demonstrate that RAGE drives tumor progression and metastasis through distinct tumor cell mechanisms, both intrinsic and extrinsic," said Hudson. "This may represent a novel and therapeutically viable approach for treating a variety of metastatic cancers, not just breast cancer."

"This is an extraordinary step in better understanding how and why breast cancer spreads," said Judy Salerno, M.D., M.S., president and CEO of Susan G. Komen, which provided a Career Catalyst Research Grant to Hudson for this research. "Dr. Hudson's work has the potential to save the lives of women and men battling metastatic disease, and we at Komen are proud to have helped launch his promising career in breast cancer research."

Researchers at the University of Michigan have identified a promising new compound for targeting one of the most aggressive types of breast cancer.

The compound, currently called UM-164, goes after a kinase known to play a role in the growth and spread of triple-negative breast cancer. UM-164 blocks the kinase c-Src and inhibits another pathway, p38, involved in this subtype. The researchers also found that the compound had very few side effects in mice.

"Triple-negative breast cancer is in dire need of new drugs. The treatments that have dramatically improved breast cancer outcomes don't apply to patients with this type of disease," says senior study author Sofia Merajver, M.D., Ph.D., scientific director of the breast oncology program at the University of Michigan Comprehensive Cancer Center.

Triple-negative breast cancer is more aggressive than other types of breast cancer. Patients are much more likely to see their cancer recur and spread. Currently there are no approved targeted therapies for triple-negative breast cancer, which represents about 20 percent of breast cancer diagnoses.

Triple-negative breast cancer is so-called because it is negative for two hormone receptors and the HER2 protein -- the three markers that current treatments have successfully targeted. That leaves chemotherapy as the only treatment option for this type of cancer.

"We are gaining a better understanding of the biology of triple-negative breast cancer, which is essential to developing targeted therapies," says study first author Rabia A. Gilani, Ph.D., a post-doctoral research fellow at U-M.

Scientists have been interested in c-Src because of its role in breast cancer progression and metastasis. But drugs designed to target c-Src have proven mostly ineffective.

The U-M team took a different approach. While other c-Src inhibitors merely try to block the kinase, UM-164 binds to it and forces the kinase to turn off. Results of their study are published in Clinical Cancer Research.

"The reason our compound works is that we have a novel mechanism for binding the kinase. It has a response similar to removing the protein entirely from the cell, as opposed to only inhibiting the activity," says senior study author Matthew B. Soellner, Ph.D., assistant professor of medicinal chemistry at the University of Michigan.

In addition to blocking c-Src, the researchers found that UM-164 inhibited p38, another kinase pathway implicated in triple-negative breast cancer. By testing an existing c-Src inhibitor individually and then combining it with an existing p38 inhibitor, they found the combination was more effective. This work was done in cells.

"They're much better together than they are individually," Soellner says. "And with our compound, the outcomes were even stronger than with the existing drugs. We weren't trying to target p38, but it turns out to be a promising target in this disease."

The researchers also found that they could administer the drug to mice at a dose that was effective against the cancer but that caused few side effects. Much more laboratory testing is needed to understand the safety profile of UM-164 before any clinical trials could be considered. The researchers plan to do additional safety testing in specialized mouse models based on tissue from patients.

A study headed by the Institute for Research in Biomedicine (IRB Barcelona) and in collaboration with hospitals around Spain and the Universitat Rovira i Virgili (URV) has unveiled breast cancer dependence on lipids. This discovery could pave the way for new therapeutic strategies to fight the disease.

In an article published in Nature Communications, the researchers report that breast cancer cells need to take up lipids from the extracellular environment in order to continue proliferating. The main protein involved in this process is LIPG, an enzyme found in the cell membrane (the layer that surrounds a cell) and without which tumour cell growth is arrested. Analyses of more than 500 clinical samples from patients with various kinds of breast tumour reveal that 85% have high levels of LIPG expression.

In Spain, breast cancer is the most common tumour in women and the fourth most common type in both sexes (data from the SEOM, 2012), registering more than 25,000 new diagnoses each year. According to figures from the World Health Organization, every year 1.38 million new cases of breast cancer are diagnosed and 458,000 people die from this disease (IARC Globocan, 2008).

Achilles Heel

It was already known that cancer cells require extracellular glucose to grow and that they reprogram their internal machinery to produce greater amounts of lipids (fats). The relevance of this study is that it reveals for the first time that tumour cells must import extracellular lipids to grow.

"This new knowledge related to metabolism could be the Achilles heel of breast cancer," explains ICREA researcher and IRB Barcelona group leader Roger Gomis, co-leader of the study together with Joan J. Guinovart, director of IRB Barcelona and professor at the University of Barcelona. Using animal models and cancer cell cultures, the scientists have demonstrated that blocking of LIPG activity arrests tumour growth.

"What is promising about this new therapeutic target is that LIPG function does not appear to be indispensable for life, so its inhibition may have fewer side effects than other treatments," explains the first author of the study, Felipe Slebe, who was funded by a "la Caixa" International PhD fellowship. Guinovart comments that, "because LIPG is a membrane protein, it is potentially easier to design a pharmacological agent to block its activity."

LIPG has "many virtues" as a target. "If a drug were found to block its activity, it could be used to develop more efficient chemotherapy treatments that are less toxic than those currently available," says Gomis.

The scientists are now looking into international collaborations in order to develop LIPG inhibitors.

Mutations are the replacement of DNA bases known as Adenine (A), Cytosine (C), Guanine (G) and Thymine (T) with other bases. When mutations such as C to T or G to A are found within a specific DNA sequence, this is known as a mutation signature. These mutation signatures are like spelling mistakes that carry signs of the agents that caused the mutations. Ultraviolet light, tobacco smoke and other cancer-causing agents leave behind such signatures in the DNA of tumors.

Recently, a new mutation signature found in cancer cells was suspected to have been created by a family of enzymes found in human cells called the APOBEC3 family. The study, "Strand-biased Cytosine deamination at the Replication Fork causes Cytosine to Thymine Mutations in Escharifier coli," led by Ashok Bhagwat, Ph.D., professor of chemistry in the College of Liberal Arts and Sciences at Wayne State University, was recently published in the Proceedings of the National Academy of Sciences.

In addition to Bhagwat, collaborators from Wayne State University and Indiana University have determined the target within DNA that is attacked by APOBEC3 enzymes. Results from this basic science research project provide an understanding of a major source of mutations that may drive tumor growth and also explains a key finding in microbial evolution.

DNA consists of two thin strands that are made up of the four bases, which are arranged in specific sequences, creating words and chapters that contain the secrets of the cell. The two DNA strands are intertwined with each other to protect the bases from damage by chemicals and enzymes. Unfortunately, the cell must copy its DNA before it can divide. This copying process requires that the two DNA strands are briefly separated, making DNA "single-stranded" and thus susceptible to damage.

According to Bhagwat, an odd quirk of DNA biochemistry is that one of the DNA strands, known as the lagging-strand template (LGST), stays single much longer than its counterpart, the leading-strand template (LDST). The WSU/IU team showed that APOBEC3 enzymes preferentially attack the LGST, causing mutations during DNA copying.

"We did this work using the simple bacterium Escherichia coli as a model, introducing the active part of the human enzyme APOBEC3G in it," said Bhagwat. "The advantage of using E. coli is that its complete DNA sequence can be easily determined and the way it copies its DNA is well understood."

Bhagwat's research team has been studying the larger AID/APOBEC family of enzymes for the past 14 years and has helped show that this family of enzymes converts C to an abnormal base called Uracil (U). The U gets repaired back to C most of the time, but sometimes this process fails and U is fixed as a T. This is called a C-to-T mutation.

Bhagwat initiated collaboration with Patricia Foster, Ph.D., at Indiana University and provided her group the A3G gene to express in E. coli. They determined the DNA sequence of hundreds of such bacteria and cataloged more than 1,000 mutations caused by A3G. Weilong Hao, Ph.D., assistant professor of biological sciences at Wayne State, later analyzed the mutations, and noticed that when A3G was in the cells, C's in the LGST were replaced with T's three to four times the frequency at which they were getting replaced in the LDST. Statistical analysis of the data showed that this occurrence was extremely unlikely to happen by chance, which means that APOBEC3 enzymes must target the LGST.

Cancer is often called a genetic disease because nearly all cancer-causing agents cause mutations. When the DNA sequence of breast tumors and other cancers was recently determined, C to T were the most frequently found mutations. These mutations were often found in clusters, suggesting that large stretches of DNA must become damaged in a single mutational event.

"These mutations had the signature of mutations caused by APOBEC3 enzymes, but it was unclear where these enzymes found the necessary long stretches of single-stranded DNA to mutate," said Bhagwat. "The work by our collaborative team has shown that during the copying of DNA, the LGST strand of DNA is accessible to APOBECs and this causes the mutations."

According to Bhagwat, bacteria like E. coli display a phenomenon called "GC skew" that is related to this discovery. Bacterial DNA typically has fewer C's in LGST than G's. In light of the results of work by WSU/IU scientists, this observation can be explained at the molecular level. Bacteria do not naturally contain APOBEC3 enzymes, but water and other cellular chemicals can also cause C to T mutations. However, they do so at a very slow rate compared to APOBECs. Despite this slowness, the bacteria have replaced many of the C's in their LGST with T's over millions of years of evolution, creating the GC skew. Thus, the act of copying DNA, which is essential to life, drives both microbial evolution and cancer development.

"Our results could have a great impact on identifying the source of mutations in many cancers and perhaps tailoring treatments based on this information," said Bhagwat. "Only some tumors have APOBEC mutational signatures and these can be identified using current DNA sequencing technology. Eventually, we may be able to treat these cancers in their early stages to prevent mutations caused by APOBEC3s."

"This study is a beautiful example of how the power of bioinformatics and genomics is valuable in addressing important biological questions," said Hao. "It has potential to make a positive impact on the health outcomes of people with cancer and possibly other diseases in the near future."

The research, published in the journal Cell Reports, shows how the expression of a protein causes mutations to accumulate in actively replicating DNA. The work is complemented by studies from other researchers published in the Proceedings of the National Academy of Sciences and Cell, which indicate that similar phenomena occur in E. coli cells and sequenced human tumors.

"It makes the overall impact of the work greater when multiple research groups work together and come to similar conclusions using different techniques," said Steven Roberts, an assistant professor in the WSU School of Molecular Biosciences who coordinated publication with the other labs.

Roberts' lab introduced the protein, an enzyme with the shorthand name of APOBEC, into a laboratory strain of the baker's yeast Saccharomyces cerevisiae. He and his colleagues then documented how it mutated genetic sequences in a small region of just three nucleotides, the subunits of DNA.

The protein normally kills viruses by making changes to their genetic sequence, inactivating them. But the protein can also change the genetic sequence of a normal cell, altering the body's blueprint and making mutations that cause cancers.

"What we found is the way that the proteins are making these mutations in tumors is they actually take advantage of the fact that tumors are dividing a lot, so they're able to damage DNA that's being actively replicated," said Roberts.

As DNA replicates, it has moments in which single strands of its double helix are exposed. The APOBEC protein takes advantage of this vulnerability to cause damage. Prior studies have found that one in five human tumors have evidence of these enzyme-induced mutations.

In addition to causing tumors, the protein can continue to mutate tumor DNA, increasing a cancer's genetic diversity and giving it a wider tool kit with which to resist treatment.

A greater knowledge of how APOBEC works could lead to treatments that decrease its activity, said Roberts. Or a treatment could go in the other direction, creating so many mutations in a tumor that it self-destructs.

Researchers at the University of California, San Diego School of Medicine have identified an enzyme that controls the spread of breast cancer. The findings, reported in the current issue of PNAS, offer hope for the leading cause of breast cancer mortality worldwide. An estimated 40,000 women in America will die of breast cancer in 2014, according to the American Cancer Society.

"The take-home message of the study is that we have found a way to target breast cancer metastasis through a pathway regulated by an enzyme," said lead author Xuefeng Wu, PhD, a postdoctoral researcher at UC San Diego.

The enzyme, called UBC13, was found to be present in breast cancer cells at two to three times the levels of normal healthy cells. Although the enzyme's role in regulating normal cell growth and healthy immune system function is well-documented, the study is among the first to show a link to the spread of breast cancer.

Specifically, Wu and colleagues with the UC San Diego Moores Cancer Center found that the enzyme regulates cancer cells' ability to transmit signals that stimulate cell growth and survival by regulating the activity of a protein called p38 which when "knocked down" prevents metastasis. Of clinical note, the researchers said a compound that inhibits the activation of p38 is already being tested for treatment of rheumatoid arthritis.

In their experiments, scientists took human breast cancer cell lines and used a lentivirus to silence the expression of both the UBC13 and p38 proteins. These altered cancer cells were then injected into the mammary tissues of mice. Although the primary tumors grew in these mice, their cancers did not spread.

"Primary tumors are not normally lethal," Wu said. "The real danger is cancer cells that have successfully left the primary site, escaped through the blood vessels and invaded new organs. It may be only a few cells that escape, but they are aggressive. Our study shows we may be able to block these cells and save lives."

Researchers have also defined a metastasis gene signature that can be used to evaluate clinical responses to cancer therapies that target the metastasis pathway.

Feb. 6, 2013 — Researchers at the University of Minnesota have uncovered a human enzyme responsible for causing DNA mutations found in the majority of breast cancers. The discovery of this enzyme -- called APOBEC3B -- may change the way breast cancer is diagnosed and treated.

The findings from a team of researchers led by Reuben Harris, Ph.D., associate professor of biochemistry, molecular biology and biophysics and also a researcher at the Masonic Cancer Center, University of Minnesota, are published in the latest edition of Nature.

"We strongly believe this discovery will change the way mutations in cancer are viewed and, hopefully, it will allow cancer researchers to develop new treatments approaches that can prevent these mutations before they become harmful," said Harris.

Harris' quest to learn more about mutations in cancer initially began with HIV research. This previous work by Harris' lab and others indicated that APOBEC3B and related enzymes function normally to protect from infectious viruses like HIV-1.

During these studies, Harris' team developed specific tests to quantify the expression of each of the seven APOBEC3 genes, including APOBEC3B.

"DNA mutations are absolutely essential for cancer development," said Harris. "Our experiments showed the APOBEC3B enzyme causes mutations in the genome of breast cancer cells. From this, we were able to reasonably conclude that the APOBEC3B is a key influencer in breast cancer."

However, Harris points out that APOBEC3B appears to be a biological "double-edged sword." It protects some cells from viruses such as HIV-1 yet produces mutations giving rise to cancer in others.

Harris stresses the need for additional research. If further studies confirm that high APOBEC3B levels indicate the early presence of breast cancer, a simple blood test could be a strategy for early detection.

Another goal for Harris is finding a way to block APOBEC3B from causing mutation, just as sunscreen prevents sun from causing mutations leading to melanoma. His collaborative HIV studies are already pointing toward such drug possibilities.

"Our next steps will focus on the connections between high levels of APOBEC3B, age and other genetic risk factors that are known breast cancer markers. Ultimately, we hope our discovery leads to better therapeutic outcomes for patients," said Harris.

Kenny is the co-author along with Bissell of a paper published in the Journal of Clinical Investigation entitled: Targeting TACE-Dependent EGFR-ligand Shedding in Breast Cancer. This paper presents the latest experimental results from an on-going investigation led by Bissell into the ecology of tumors.

It has long been Bissell’s contention that “no tumor is an island.” Tumor cells, she maintains, exist in the same microenvironment as healthy cells and must therefore appropriate normal physiological processes to facilitate their growth and spread. As she and her colleagues have repeatedly demonstrated, this idea can open up potential new avenues and targets for diagnostic and therapeutic applications.

For this latest paper, Kenny and Bissell looked into the pathway by which the EGFR signal is carried. EGFR, which stands for Epidermal Growth Factor Receptor, is the protein on the outer surface of a cell that is activated by EGF and related growth factors and signals for the cell to divide. Given that one of the hallmarks of cancer is cell division run amok, the reduction of high levels of EGFR activity has long been a primary target for anti-cancer drug development. So far, however, drugs aimed at directly inhibiting EGFR activity have met with only limited success in the cancer clinic, primarily in a small number of lung cancers.

“Because of this, we turned our attention to the processes that regulate the production of the ligands which bind and activate EGFR,” Kenny said. “We reasoned that this binding and activation is essential for EGFR activation and that finding a way to block this interaction might prove to be an important additional approach to explore for inhibition of this pathway.”

Earlier studies had indicated that TACE (tumor necrosis factor-alpha-converting enzyme) acts like a “molecular scissors” that releases from the cell surface a pair of ligands, called Amphiregulin and TGF-alpha, which activate EGFR. Bissell and Kenny found that by targeting TACE (also known as ADAM17) with either molecular inhibitors or short interfering RNAs (siRNAs) that silence the TACE gene, they could effectively block the shedding of Amphiregulin and TGF-alpha ligands. This resulted in the inhibition of EGFR signaling and the reversion of malignant characteristics in tumor cells. It is the first reported use of protease inhibitors to stop breast cancer cell proliferation and restore the normal breast tissue structure.

“We have designed an entirely new way of targeting EGFR signaling in breast cancer,” said Kenny. “Almost all the work to date has involved the use of antibodies that stick to kinases or drugs that block kinase activities.”

These newest results are very much in keeping with Bissell’s contention that cancer growth and spread is not solely a tumor cell-autonomous process brought on by a genetic mutation. Bissell is one of the leading proponents of the idea that a cell’s genetic information is supplemented by contextual information encoded within the microenvironment that surrounds the cell.

“It is becoming increasingly apparent that, as with other organs, the biogenesis of the tumor represents an interaction between the tumor cell, other types of cells and the rest of the microenvironment,” she said.

Kenny and Bissell successfully tested their protease blocking approach on several different breast cancer cell lines. In addition, they examined the data from 295 breast cancer patients and found that tumors which produced the highest levels of TACE and the TGF-alpha ligand posed the greatest risk to women.

“Women with those types of tumors would seem to be poorly served by existing treatments and may stand to benefit from therapies that are based on the inhibition of TACE activity,” said Kenny. “We would like to see some of the companies who have developed the new generation TACE inhibitors for treatment of rheumatoid arthritis also consider evaluating them in cancer patients.”

Kenny stressed that the importance of EGFR to so many different tumor types, including lung, head and neck, bladder, colorectal and kidney, makes it likely that “TACE inhibition has the potential to be an effective means of stopping tumor growth for EGFR-dependent cancers outside the breast as well.”

This research was supported by grants and a Distinguished Fellowship Award from the U.S. Department of Energy’s Office of Biological and Environmental Research, the National Cancer Institute,and an Innovator award from the U.S. Department of Defense’s Breast Cancer Research Program to Bissell, and by a Susan G. Komen Breast Cancer Foundation fellowship to Kenny.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our Website at http://www.lbl.gov.